Progress toward the development of genetically modified mosquito (GMM) strains to be used in a genetic control program for mosquito vectors of malaria has reached a point where most of the scientific community involved in this research are beginning to think about field trials. The following recommendation was made by a group of experts in the field of vector biology participating in a meeting entitled "Genetically Engineered Arthropod Vectors of Human Infectious Diseases": "The exciting progress in molecular strategies for blocking parasite development in vectors has far outpaced the related and essential work on field sites and vector populations that must precede any GM release field trial." Imperial College, London 14-15 September, 2001. We believe that the most promising sites for GMM field trial sites would be on islands off the coast of sub-Saharan Africa. With this Exploratory! Developmental Research Grant proposal (R21) we seek support to initiate studies aimed at assessing the suitability of two island sites. We have selected one island off the east coast of Africa and one off the west to explore for this grant application. Based on a critical analysis of available data we chose to study Anopheles gambiae populations on Isla de Orango, part of the Bijago Archipelago in West Africa and Grande Comore in East Africa. Our initial assessment will include: (1) collection of basic ecological and biological data for An. gambiae at each site, including relative population densities and adult distribution; (2) an assessment of the degree to which island populations are genetically isolated from the nearest mainland populations and from populations on neighboring islands, and a description of the genetic structure of populations on each of the two target islands; (3) creation of a GIS system that describes the ecology of each site and is fully integrated with information from the ecology and population genetics studies.